Manufacture of phosphoric acid



Mam}? 1932- l. HECHENBLEIKNER 39 L MANUFACTURE OF PHOSPHORIC ACID Filed Feb. 25, 1930 v ICONCENTRATED SULPHURIC ACID WATER OR WEAK l PHosPHomc ACID WATER Si- RAY GROUND QSEQ fiTRONG, HOT SUL! 'HURIC ACID" 50 AND Man;

FUME ABSORPTION A -M Q TOWER u L WEAK SOLUTION I MiXER PHOsFHomc ACID M m m H AGITATOR To F'lLTER AND WASPHNG EQLHP- J MENT XNVENTOR I Patented r UNITED STATES PATENT orrlca I INGENUIN HECHENBLEIKNER, O11 CHARLOTTE, NORTH CAROLINA, ASSIGNOR TO CHEMICAL CONSTRUCTION CORPORATION, 01' CHARLOTTE, NORTH CAROLINA, A

CORPORATION OF DELAWARE MANUFACTURE OF PHOSPHORIG ACID Application 11:11 February 25,? 1980. Serial Ho. 431,177.

This invention relates to the manufacture of phosphoric acid, and more articularly to a method and means for menu acturing phosphoric acid from phosphate rock and sul- 6 phuric acid.

One of the known methods of manufacturing phosphoric acid'from phosphate rock is by the sulphuric acid route. In this method the hosphate rock, which largely contains 10, calcium salts of. hosphoric acid, is reduced by treatment wit phosphoric acid and then caused to react with sulphuric acid in order to obtain calcium sulphate and phosphorlc acid; From the resulting mixture or slurry 1 1 the phosphoric acid is'separated.

Considerable trouble and difiiculty arises in the practice of thisinethod when using phosphate rock containing a hi h percentage of compounds of fluorine. he fluorine forms a hydrofluo-silicic acid which. is deposited on surfaces in the form of a hard crusty formation. This formation builds up on the various ieces of apparatus used in the plant, and ten s to stop up pipe lines and the like. Furthermore, fluorine or its acids react with and cause undesirable disintegration of lead and other of the construction materials used in the plant apparatus. The

primary object of the present invention is to,

30 overcome this difliculty, and this is accomplished, generally speaking, by eliminating fluorine and the acids thereof in the first stage of the operation of the plant. I have found that by treating the ground phosphate rock first with sulphuric acid, and especially with hot sulphuric acid of a desired concentration, the acid will react with the rock to release fluorine compounds, particularly hydrofluoric acid or hydrogen fluoride in gaseous form, and the resulting gases may be carried 01f from the mixture, thereby freeing the remainder of the phosphoric acid manufacturing plant from the difficulties above mentioned. I

The manufacturin process as usually ap plied requires consi erable expensive apparatus because a number of mixers and large expensive agitators are needed in which the desired reaction takes place in successive stages. One of the objects of my invention is to reduce the amount of apparatus 'required, and this desirable reduction in appatus is also made possible by the changed'process above outlined because when strong hot sulphuric acid is used with ground or comminuted phosphate rock the reactioriis completed in the first mixing.

Still another object of my invention is to obtain the desired supply of hot sulphuric acid with practically, no cost for heating the same. Sulphuric acid is used which is greater in concentration thanis desired for the present reaction, this strong acid being readily obtained, for example, from manufacture by the contact process, and the strong acid is diluted to the desired concentration by water or a Weak solution of phosphoric acid. The mixing of the strong acid with water generates considerable heat, and in this way hot sulphuric acid of the desired concentration is obtained without using concentrators and without using heating equipment.

The desired phosphoric acid is obtained by separating it from the mixture of calcium sulphate and phosphoric acid, which results from the reaction previously outlined. Still another object of the present invention is to facilitate this separation, and to this end the mixture has added thereto a weak solution of phosphoric acid in order to give the mixture a strength and consistency best suited for the separation stage.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the method and the apparatus elements and their relation one to the other as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing, the single figure of which is a schematic or flow diagram ,of the reaction stage of the process.

The manufacture of phosphoric acid by the sulphuric acid route may, in general, be divided into two stages, a reaction stage, and a separation stage. My invention deals more particularly with the reaction stage and inasmuch as the separation stage may coincide with that already used in this art, the draw- 10 ing discloses the flow relations in only the first or reaction stage of the process.

The phosphate rock is first broken up and then ground in a suitable grinding mill after which the ground rock may be fed to a mixer. This has been indicated in simple form in the accompanyin drawing by a hopper A, acting as a source 0 ground phosphate rock, which may be fed as desired to a mixer B. The ground rock is mixed directly with hot sulphuric acid supplied from a tank C to the mixer B. This sulphuric acid should have a concentration of 50 degrees Baum or more in addition to being hot, and under these conditions I have found that the reaction proceeds favorably and rapidly with the evolution of practically all of the fluorine contained in the phosphate rock, ordinarily in the form of hydrogen fluoride or hydrofluoric acid. The gases escaping from the mixer B may be led to a washing tower or fume absorption tower D, from which the hydrofluoric acid may, if desired, be recovered.

The acid in the tank C is preferably obtained by mixin sulphuric acid of greater concentration, w ich may readily and economically be obtained by the contact process of manufacturing sulphuric acid, and which is indicated as supplied from a tank E, with water or, if desired, with weak phosphoric acid, which may be obtained from the washing apparatus ordinarily used in the separation stage of the plant and here indicated as supplied through a pipe F. The mixture is ma e in proper proportion to make the acid in the tank C of the desired concentration, and at the same time suflicient heat is evolved to bring the acid to the desired temperature preparatory to its use in the mixer B.

The mixer B may be a standard mixer, and the ground hosphate rock from the ho per A and the ot strong sulphuric acid rom the tank C are mixed together in the mixer B in proper proportions for leaching out all of the phosphoric acid in the rock. This reaction takes place in a single stage, thereby economizing 1n apparatus and avoiding having this reaction continue in the agitator, as well as dispensing with the necessity of having a plurality of agitators. In the present arrangement a single agitator indicated at G is suflicient, and the contents from the mixer B are emptied into the agitator G at suitable times when the reaction is completed.

The agitator G may be of conventional type and is supplied with a weak solution of phosphoric acid from the tank H. The object of mixing the slurry with the weak phosphoric acid is to give the mixture in the agitator a desired strength and consistency most suitable for conveying it to the separation stage of the plant, which is done through the conduit J.

The separation stage may be of customary -Part or all of this wash water or weak phosphoric acid may be supplied to either or both of the elements F and H above described, for mixture with the strong sulphuric acid, or with the rock mixture or slurry preparatory to the filtration of phosphoric acid therefrom.

The method of practicing my invention, the necessary apparatus therefor, and the advantages of the invention will in the main be apparent from the foregoing description thereof. The fluorine is removed from the phosphate rock, and this removal is accomplished at the very be 'nning of the process, thereby obviating t e extremely troublesome difficulties heretofore caused thereby. The removal of the fluorine is accomplished without adding extra steps to the hosphoric acid manufacturing process an in fact while reducing the number of steps used therein and the apparatus necessary for the practice of the process, because the hot concentrated sulphuric acid mixed directly wit-h the ground phosphate rock not only releases the fluorine, but also yields phosphoric acid from the phosphate rock in a more rapid and eflicient manner than has heretofore been the case. The desired hot concentrated sulphuric acid may be obtained in a simple manner by diluting more concentrated acid.

In some of the appended claims I shall refer to the fluorine generally, b which I mean to include fluorine compoun s and particilarly hydrogen fluoride or hydrofluoric aci It will be apparent that while I have shown and described my invention in the preferred form, many changes and modifications may be made in the method and apparatus disclosed without departing from the spirit of the invention, defined in the following claims.

I claim:

1. In the manufacture of phosphoric acid from phosphate rock by a process generally resembling the Dorr process, the said phosphate rock containing a relatively high percentage of fluorine compounds, the method of initially removing the fluorine in order to prevent fouling of the apparatus by fluorine compounds, and of quickening the process and simplifying the process and apparatus therefor, which includes grindin the rock, mixing the ground rock directly with hot concentrated sulphuric acid of Baum or more in a single mixing stage, withdrawing all of the resulting fumes from the mixing stage, agitating the slurry from the mixer and adding'thereto a weak solution of phosphoric acid in order to obtain a desired strength and consistency of mixture, and

finally separating the phosphoric acid from the mixture.

2. In the manufacture of phosphoric acid from phosphate rock by a process generally resembling the Dorr process, the said phos- .phate rock containing a relatively high percentage of fluorine compounds, the method of initially removing the fluorine in order to prevent fouling of the apparatus by fluorine compounds, and of recovering the fluorine, and of quickening the process and simplify r ing the process and apparatus therefor, which v includes grindin therock,mixingthe ound rock directly wit hot concentrated su ph'uric acid of 50 Baumor more in a single mixing sta e, withdrawing all of the resulting H fumes rom the mixing stage and passing the a same through a fume absorption tower, agitating the slurry from the mixer in a single agitator stage and addin thereto a weak so lution of phosphoric aci in order to obtain a desired strength and consistencyof mixture, and finally separating the phosphoric acid from the mixture. e

3. In the manufacture of phosphoric acid fromphosphate rock by aprocess generally resemblin jthe Dorr process, the said phosphate roc containing a relatively high percentage of fluorine compounds, the method of initially removing the fluorine in order to preventfouling of the apparatus byfiuorine compounds, and'of quickening the process and simplifying the process and apparatus therefor, which includes grindin the rock, mixing very highly concentra sulphuric acid with an aqueous liquid in order to obtain 40 hot sulphuric acid having a concentration of Baum or more, mixing the ground rock directly with the resulting hot concentrated sulphuric acid in a single mixing stage, withdrawing all of the resulting fumes from 45 the mixing stage, agitating the slurry from the mixer in a single agitator stage and adding thereto a weak solution of phosphoric acid in order to obtain a desired strength and consistency of mixture, and finally separat- 60 in the phos horic acid from the mixture.

, %igned at harlotte, in the county of Meeklenberg and State of North Carolina, this 21 day of February A. D. 1930.

INGENUIN HEGHENBLEIKNER. 

